BELMONT & CESSNOCK WASTEWATER TREATMENT PLANT INLET WORKS REMEDIATION

Concept and Objectives of the Project

Hunter Water Corporation and Hunter H2O worked in partnership to implement urgent remediation of inlet works structures at Belmont and Cessnock Wastewater Treatment Works. These structures had suffered severe concrete degradation from long-term exposure to hydrogen sulphide gas (H2S) arising from turbulent sewage which flowed in continuously 24 hours per day, 365 days per year.

The project objectives were to urgently:

  • mitigate immediate WHS risks associated with risk of structural collapse
  • mitigate environmental / treatment plant failure risks from spalling concrete and failure of process and hydraulic equipment
  • refurbish equipment and provide protection extend the longevity of structures to 2031
  • Each structure usually operated and received flow from complex networks of (up to fifteen) wastewater pumping stations. It was not possible to hold back the flow in the network during the daytime. The only opportunity to attenuate flows was for 2-4 hours at a time, between midnight and 6am when there were favourable antecedent weather conditions.

 

Project Planning and Development

Given the significant operational and hydraulic challenges, achievement of these objectives required a very high level of planning and engineering thought. A combination of strategies were selected to address specific operational and environmental conditions at each part of the asset. These broadly included:

  • firstly undertaking hydraulic modelling and operational trials during the night to assess feasible shutdown periods (and the risk factors that could cause influxes of these inflows)
  • survey, design, manufacture and overnight installation of prefabricated steel liners via cranes and fast-setting grout which was remotely injected (without entry of personnel) for urgent repairs to the most degraded sections
  • design and staged implementation of temporary bypass strategies using large diameter pipework – this was required to facilitate isolation / drainage of structures by diverting flows into adjacent treatment plant structures to enable entry for manual remediation
  • selection of remediation technologies (intercrete), lining products (polibrid) and application methodologies that would facilitate concrete repair and lining within short periods given the particular corrosion and environmental conditions that existed at each site.

Given the risk profile, the evaluation of engineering options was undertaken using a consultative process with stakeholders from Hunter Water’s Network Operations / Project Delivery and Hunter H2O’s design and construction teams / subcontractors. Each option was reviewed using a multi-criteria analysis which considered safety, environmental & operational risk, community impacts, quality, capital cost and time for completion. Detailed Safety in Design workshops were also held.

The installation of sleeves and bypass pipework during 2 hour shutdown windows carried such a high degree of operational and safety risk that they were programmed in minute detail (15 minute increments). Contingent plans put in place to enable safe evacuation of the inlet works without overflows in the event that works were not completed.  Each shutdown required a co-ordinated, simultaneous inhibition of up to seven wastewater pump stations and a very detailed procedure for management of confined space entry / engulfment risks across three separate teams.

Due to the geographic remoteness of the pump stations, new practices were developed, trialled and proven to ensure that safe confined space entry would be achieved without conventional lock-out systems. In addition to radio communication and detailed monitoring of real-time SCADA records, SMS technology was used for photographing and proving hydraulic lock-outs, communicating warnings to personnel entering confined spaces to prevent any risk of them being engulfed in sewer inflows.

Outcomes

Seventeen shutdowns were undertaken altogether in intense, nightly shifts over several months. Contractor entry into the inlet works was successfully managed without any safety incidents and the concrete refurbishment works were undertaken to a high standard. The documented isolation procedure was followed meticulously on every occasion.

The project was delivered safely on time and under budget and has set a precedent for shutdown methodologies and similar remediation projects.

External Organisations Involved:

The majority of the works were delivered under a partnering EPCM contract by Hunter Water and Hunter H2O under a collaborative Engineering, Procurement and Construction Management (EPCM) arrangement. 

Other key subcontractors and stakeholders involved with the project

  • Veolia – Treatment Operations during the project
  • Alfabs – Civil Construction Contractor on the project
  • SGM – stainless steel sleeve manufacture and installation
  • LJ Pfeiffer Coatings – Concrete Repair Contractor on the project
X
Enter your Hunter H2O Holdings Pty Limited username.
Enter the password that accompanies your username.
To prevent automated spam submissions leave this field empty.
Loading